Method for separating electrically charged particles



June 19, 1962 M. J. HIGATSBERGER 3, 0,

METHOD FOR SEPARATING ELECTRICALLY CHARGED PARTICLES INVENTOR H .QIHzLgaia bezyer ATTO R N EYS June 19, 1962 M. J. HIGATSBERGER 3,040,173

METHOD FOR SEPARATING ELECTRICALLY CHARGED PARTICLES Filed June 5, 1958 2 Sheet's-SheetZ PHASE CONDITIONS IN MODULATOR.

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I ATTORNEYS United States Patent Gffice 3,040,173 Patented June 19, 1962 METHOD FOR SEPARATING ELECTRICALLY CHARGED PARTICLES Michael J. Higatsberger, Vienna, Austria, assignor to Osterreichische Studiengesellschaft fiir Atomenergie Ges.m.b.H., Vienna, Austria, an Austrian firm Filed June 5, 1958, Ser. No. 749,014 Claims priority, application Austria June 6, 1957 4 Claims. (Cl. 25041.9)

This invention relates to a method of separating electrically charged particles, particularly of isotopes, with the aid of electric fields, which method is characterized in that the particles are subjected to the action of alternating fields and are then deflected by electrostatic fields.

For the calculation of the nuclear bonding energy it is desired in nuclear physics to determine the nuclear mass as accurately as possible. At the present time the mass of nuclides can be determined by any of four methods, which are independent of each other. These are mass spectroscopy, nuclear reactions, beta and gamma ray spectroscopy and microwave spectroscopy.

Mass spectroscopy using combined electric and magnetic fields occupies an eminent position among these methods. Whereas progress regarding a precise determination of nuclear masses has recently been achieved, there are still inconsistencies, which become apparent when the results of the various methods are compared and in measurements made with the same methods by diiierent Workers.

Hereinafter a mass spectrometer according to the in vention will be proposed which is free of magnetic fields and for this reason has no system errors due to the magnetic field.

FIG; 1 is a schematic side elevation of one form of the invention.

FIG. 2 is a schematic View, to a larger scale, of the geometry of one of the modulating sections of FIG. 1, with formulas explaining that geometry.

FIG. 3 is a view similar to FIG. 1 of a modified arrangement.

A typical arrangement in accordance with the invention is shown in FIG. 1, in which a parallel beam of ions 1 enters with a constant kinetic energy into a plate condenser at the entrance angle The condenser consists of three parallel plates, arranged to form in efiect two parallel-plate condensers in face-Wise adjacency, with a common intermediate electrode; the outer plates 2 of which are positively charged whereas the intermediate plate, which consists actually of two plates 3 and 4 spaced from each other by several millimeters, is grounded (at 5 In such a system a beam 1 of positive ions is deflected according to a parabola toward the grounded plate 3, 4 and impinges on this plate at a point determined by the kinetic energy of the ions, the entrance angle, and the positive deflecting potential.

The grounded plates 3, 4 are provided at the points of impact with slots 6, through which the beam of ions can pass over into the other field system, where it is reflected as by a mirror. Additional three-plate systems (modulators M1, M2, M3) are disposed adjacent to the slots 6 between the two grounded plates 3, 4. The intermediate panels 7 of these modulators are at a suitable high-frequency potential Whereas the two outer plates 8, 9 are grounded. After the second deflection, ions which gain energy from the high-frequency field will impinge on the grounded plate 3 or 4 at a diflerent point than the ions which have not gained energy. The following slots 6 are arranged so that only ions having a maximum energy gain can pass. According to FIG. 1 the equation of motion gives V x=4a S1l1-oe COS-a VA and V a s1n -a y VA wherein V is the accelerating voltage, V the deflecting voltage, both in volts, or the entrance angle and a the plate spacing in centimetres.

When it isassumed that a group of ions gains in each modulator the fraction of energy BV the coordinates after the nth modulator will be:

n=0, 1, 2, The transit time between the individual modulators is found to be wherein m and e, respectively, are the mass and charge expressed in electrostatic units.

It is also apparent from FIG. 1 that where only three modulators are provided, equal transit times Will be obtained on the paths x and x if the deflecting potential or the distance a is corrected at a deflecting plate according to equation (3) with the factor (1+n15') It is obvious that consideration must be given to the resulting x-coordinates and the different geometry of the slot arrangement must be taken into account. The path x depends only on the geometry of the slot at the collector C rather than on the transit time.

Phase Conditions in Modulator It is apparent from FIG. 2 that the energy gain AW It is immediately apparent that AW has a maximum for wt+=r and Thus um w v 4 gives a frequency of for V =1000 volts and d=5 mm.

8.2 mc./s. are obtained for a mass M=l and 475 kc./s. for a mass M=300.

Resolving Power The resolving power of the instrument is determined KJTJ Af t mod and A is the fraction of a cycle between two peaks at half amplitude. A depends mainly on the Width of the slot. Where three modulators are provided the dissolving power should be quite comparable to that of instruments known per se.

Essential advantages of the present instrument over the known equipment can be seen in the elimination of the magnetic field and in the possibility of adjusting the spacing between the following modulator plates so as to continually take the additional energy gain and the resulting variations in the transit time between the modulator plates into account. If the accelerating and deflecting voltages are taken from the same high-voltage source the resolving power will not be affected by slow voltage variations. If it was desired to use more than three modulators, an insertion of delay lines between the several modulators should be considered.

FIG. 3 illustrates the invention in conjunction with a curved condenser, e.g., a cylindrical condenser. M1, M2, M3 designate again the modulators. Three cylindrical condensers are arranged one behind the other. The plates 11 are at a positive potential, the plates 12 at a negative potential. For resolving, either these voltages may be different for the successive cylindrical condensers and/ or the radii of curvature 13-17 may vary. From the explanations given hereinbefore the function of the device shown in FIG. 3 is self-explanatory. In advantageous manner the path of the particles to be resolved lies here substantially parallel to the curved plates, whereby the adjustment is facilitated. In this form of the invention, the beam also traverses successive fields produced by condenser-electrode units, but the successive condensers are in edge-wise adjacent relationship, rather than face-Wise as in FIG. 1.

The method described and the equipment for carrying it out are not only suitable for a precise mass determination but also for determining the relative frequency of the particles to be investigated, particularly of isotopes.

I claim:

1. In charged particle mass spectroscopy, the method of separating patricles of specified mass from a heterogeneous beam, comprising directing the beam at an angle through successive oppositely directed fixed pure electrostatic fields to define a serpentine beam path, and applying to said beam a cumulative velocity-modulating pure alternating electric field only during each of several successive transits thereof across the boundaries between said successive fixed fields.

2. A mass spectrometer comprising opposed plate electrodes defining successive regions for the application of fixed electrostatic fields to an ion beam traversing such regions, means for applying D.C. potential to said plates to establish oppositely directed fields in the successive regions, means for directing anion beam in succession through said regions, slotted-plate velocity-modulation electrode sets disposed at the boundaries between successive regions, means for applying to at least one such electrode of each set a high frequency potential of amplitude, phase and frequency values such as to produce successive transists across all of said boundaries only for ions of a particular smallmassrangefand target-means for collecting ions which have traversed all of said regions.

3. A mass spectrometer in accordance with claim 2, in which said opposed plate electrodes are formed as face- Wise adjacent parallel-plate condensers having their proximate plates spaced and at one D.C. polarity with respect to their distal plates, said proximate plates being apertured at spaced points to pass the ion beam from one condenser to the other, and in which said slotted-plate velocity-modulation electrode sets are posiL oned between said proximate Walls at said apertures.

4. A mass spectrometer in accordance with claim 2, in which said opposed plate electrodes are formed as edge-wise adjacent parallel-plate condensers having alternate opposite D.C. polarit, and in which said slottedplate velocity-modulation electrode sets are positioned in the edge-Wise space between said condensers.

References Cited in the file of this patent UNITED STATES PATENT S 2,615,135 Glenn Oct. 21, 1952 2,721,271 Bennett Oct. 18, 1955 2,769,093 Hare et a1 Oct. 30, 1956 2,836,759 Colgate May 27, 1958 2,957,985 Brubaker Oct. 25, 1960 OTHER REFERENCES Advances in Electronics and Electron Physics, vol. VIII, 1956, Academic Press, N.Y., pages 19798 relied on.

Smith et al.: Review of Scientific Instruments, vol. 27, No. 8, August 1956, pages 638 to 649.

Bierman: Article entitled Resonance Mass Selector, Review of Scientific Instruments, vol. 28, N o. 11, November 1957, pages 910 to 913. 

